According to estimates from the U.S. Centers for Disease and Controls (CDC), food born pathogens account for 756 million illnesses, 325,000 hospitalizations, and 5000 deaths each year in the U.S. Moreover, fresh produce is catching up with ground beef as a major source of E. coli 0157 H7 and with chicken as a major source of Salmonella. Fresh-cut produce is one of the fastest growing sectors of the fresh produce industry. Processing produce into fresh-cut form increases the risk of bacterial contamination and growth because the natural external barrier of the produce is broken by peeling, slicing, coring, trimming, and mashing.
This is also true for Ready-to-Eat (RTE) products for which starting from generally a stabilized raw material, more than 60% of the lifespan of the product can be lost because of these preparation and repackaging steps. For example, a raw block of ham packed under vacuum generally has a lifespan of 90 days whereas sliced ham stored under similar conditions seldom reaches more than 30 days even by following all the hygienic conditions. Hence there is a need for a process which can be applied after the food is processed to reduce or destroy microorganisms just before it is packaged for the preservation of the quality and shelf-life.
The importance of preserving food quality while providing safety is well known and has led to increased interest in nonthermal processing of meat, poultry, and dairy products, produce and beverage. Some of the nonthermal based technologies include high presses processing (HPP), treatment with electric pulse field, irradiation, ultrasonic, etc.
In recent years, nonthermal plasma (also referred to as so-called “cold plasma” or “non-equilibrium plasma”) has been investigated to sanitize food products. A plasma is an ionized gas which is formed by the passage of energy, for example by applying a high continuous or alternative voltage to it, or by providing energy in other forms such as microwave, radiation, laser light, or by other means. Compared to gas in its natural state, plasma contains free charged particles, electrons and ions, although it is overall electrically neutral. A nonthermal plasma is in general any plasma which is not in thermodynamic equilibrium, either because the ion temperature is different from the electron temperature, or because the velocity distribution of one of the species does not follow a Maxwell-Boltzmann distribution. As opposed to thermal plasmas where all particles of the medium (neutral molecules, atoms and radicals, ions and electrons have roughly the same energy distribution (meaning a common temperature), in nonthermal plasma electrons have a much higher average energy than heavy species. A limit to such a situation is with the so called cold plasma, corresponding to gas temperature (meaning average energy of the heavy species) is close to ambient. However there may exist plasmas that are nonthermal but not cold, with heavy species temperature less than one order of magnitude below electron temperature. In general such plasmas are sustained by electrical discharges in a gas close to atmospheric pressure and must be distinguished from other mature, industrially applied plasma technologies like welding, cutting and thermal spraying.
For nonthermal plasma, free electrons are excited by the means described above, namely acceleration by the electric field imposed by the external source of excitation. In parallel to this acceleration, electrons undergo random frequent elastic collisions with the molecules and ions, also called heavy particles. Thus electrons continuously gain energy over time in the form of a disordered motion that has similarities with thermal agitation, but is “forced” by electrical energy input and much more intense. The average electron energy corresponds to an equivalent temperature of the order of tens of thousands of degrees. The average energy of electrons is much higher than the heavy particles. If the collisions are not too frequent, in the case of a rarefied gas, for example, they transfer only little energy to the heavy particles and preserve their movement of thermal agitation corresponding to the ambient. If the electrons acquire a very high “temperature” (i.e. average agitation energy) of the order of 104 K they produce inelastic collisions with the heavy particles that produces excitation (in terms of electronic level or vibrational quantified level), ionization (that constantly replenishes the population of electrons and ions to sustain a steady plasma), or dissociation into smaller fragments, atoms and radicals. The excited particles conceal very high “chemical energy” and can be reactive enough to produce surface treatments to a material, without the need to heat the material.
In particular, it is known that cold plasma can destroy, or at least irreversibly inactivate microorganisms.
On the other hand, Modified Atmosphere Packaging (MAP) or controlled atmosphere packaging is a known technique used to extend the shelf-life of fresh or ready-to-eat food products. In this technique, the air surrounding the food in the package is removed partially or entirely and replaced by another gas or gas mixture. The effects of MAP are based on the often observed slowing of plant respiration in low O2 environment. The commonly used gases in MAP are N2, CO2 O2, rare gases (such as Ar), and their mixtures.
There is provided a method for sanitation and preservation of foodstuffs that comprises the following steps. A container containing a foodstuff is provided. A non-thermal plasma is introduced to an interior of the container. The container is sealed.
The method may include one or more of the following aspects:                the container is sealed while containing the non-thermal plasma or the non-thermal plasma in a de-excited state.        the non-thermal plasma is generated from a treatment gas selected from the group consisting of N2, CO2 O2, Ar, Xe, Kr, He, Ne, N2O, H2, H2O2, CO, NO, and mixtures thereof.        a secondary gas is introduced to the interior of the container without displacing all of the non-thermal plasma or all of the non-thermal plasma in a de-excited state, wherein the container is sealed while containing the secondary gas and non-thermal plasma or de-excited non-thermal plasma.        the non-thermal plasma is generated from a treatment gas selected from the group consisting of N2, CO2 O2, Ar, Xe, Kr, He, Ne, N2O, H2, H2O2, CO, NO, and mixtures thereof.        the secondary gas is selected from the group consisting of N2, CO2 O2, Ar, Xe, Kr, He, Ne, N2O, H2, H2O2, CO, NO, and mixtures thereof; and the secondary gas is compositionally different from the non-thermal plasma.        all of the non-thermal plasma or all of the non-thermal plasma in a de-excited state is removed and a shelf-life extending gas is introduced into the interior of the container, wherein the container is sealed while containing the shelf-life extending gas.        the shelf-life extending gas selected from the group consisting of N2, CO2 O2, Ar, Xe, Kr, He, Ne, N2O, H2, and mixtures thereof.        the non-thermal plasma or the de-excited non-thermal plasma is removed by application of vacuum to the container interior.        the non-thermal plasma or the de-excited non-thermal plasma is purged from the container interior by the introduction of the shelf-life extending gas.        the non-thermal plasma or the non-thermal plasma in a de-excited state is removed with application of vacuum to the container interior, wherein the container is sealed under vacuum.        moisture is combined with the non-thermal plasma.        the treatment gas is selected from the group consisting of H2, a mixture of H2 and He, a mixture of H2 and Ar, a mixture of H2 and CO, a mixture of H2 and H2O2, a mixture of H2 and air, and a mixture of H2 and N2O.        said step of introducing a non-thermal plasma to an interior of the container is performed inside a food packaging machine.        the food packaging machine is a flow pack type food packaging machine.        the food packaging machine is a tray type food packaging machine.        the non-thermal plasma is generated with a non-thermal plasma generation device located outside the food packaging machine and the non-thermal plasma is conveyed from the non-thermal plasma generation device to the interior of the container.        the food packaging machine is a flow pack type food packaging machine, the container is a thin plastic tubular film, and the non-thermal plasma is introduced into the interior of the tubular film with a nozzle.        the food packaging machine is a tray type food packaging machine.        the food packaging machine is a tray type food packaging machine and the non-thermal plasma is generated with a non-thermal plasma generating device comprising at least one planar microwave power applicator disposed in a lid of the tray type food packaging machine.        the food packaging machine is a tray type food packaging machine and the non-thermal plasma is generated with a non-thermal plasma generating device comprising at least one planar microwave power applicator disposed in or on the container.        the the non-thermal plasma generating device comprises at least one planar microwave power applicator        said non-thermal plasma is in sustained contact with the foodstuff for a period of time of 0.1 sec to 600 seconds.        said non-thermal plasma is in sustained contact with the foodstuff for a period of time of 5 to 60 seconds.        a vacuum is applied to an interior of the container before said step of introducing the non-thermal plasma.        a biocide is introduced into the container interior before, during or after the introduction of the non-thermal plasma into the container interior.        the biocide is particulate Silver.        